Problem: William is 45 years old and Kevin is 3 years old. How many years will it take until William is only 4 times as old as Kevin?
Solution: We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, William will be $45 + y$ years old and Kevin will be $3 + y$ years old. At that time, William will be 4 times as old as Kevin. Writing this information as an equation, we get: $45 + y = 4 (3 + y)$ Simplifying the right side of this equation, we get: $45 + y = 12 + 4 y$ Solving for $y$ , we get: $3 y = 33$ $y = 11$.